1. Field of the Invention
The present invention relates to a method of inspecting a contamination on an exposure mask used to fabricate an IC (Integrated Circuit), a LSI (Large Scale Integration) and the like and a system therefor, more particularly, relates to a method of inspecting a contamination on a rear face of an exposure mask and a system therefor.
2. Description of the Related Art
Conventionally, there is a technique to inspect a contamination on an exposure mask such as disclosed in Japan Patent Application Laid-Open No. 61-61420 in 1986. In this publication, a laser beam falls on an exposure mask perpendicularly so as to transmit through the exposure mask, and a contamination only on a transmission area is found out by detecting a scattered light which the transmitted light is scattered by a contamination such as dust. A contamination on a rear face is also detected similarly.
In the above-mentioned method, however, since an exposure light is focused on a front face of the exposure mask during exposure, a defocus occurs on the rear face of the mask. Thus, it is impossible to determine whether the size of the contamination detected on the rear face of the exposure mask actually influences on a wafer during transfer (exposure) or not. In this case, there is no choice, but it is determined by experience, or it is determined whether a contamination on the rear face of the exposure mask influences on exposure or not by transferring the mask to a the wafer in practice. Thus, there is a trouble that the detected contamination is judged by the size thereof, and there is a problem that it is impossible to supply good exposure masks efficiently since bad masks are removed after exposing in practice.
Moreover, there is a possibility that a contamination on a rear face of a shade pattern moves into the transmission area by some shock, therefore, it is necessary to detect a contamination not only in the transmission area of the exposure mask but also on the front or rear face of the shade pattern.
Thus, it is desired to detect only a contamination which actually influences on a wafer among contaminations on the rear face of the exposure mask.